Transparent conducting zinc oxide thin films doped with aluminum and molybdenum

Abstract

Undoped ZnO, ZnO:Al (0.5, 1, and 2wt% Al2O3⁠), and ZnO:Mo (⁠2wt% Mo) films were deposited by radio-frequency magnetron sputtering. Optimal deposition temperature was found to be ∼200°C for all films. Electron mobilities of 48cm2V−1s−1 were achieved for undoped ZnO films using a sputtering gas with H2∕Ar ratio of 0.3%; corresponding carrier concentrations were ∼3×1019cm−3⁠. A target incorporating 0.5wt% Al2O3 in ZnO yielded films with mobility of 36cm2V−1s−1 and carrier concentration of 3.4×1020cm−3⁠. These films present comparable conductivity and lower free-carrier absorption than films grown from a target containing 2wt% Al2O3⁠. Mo was found to be an n-type dopant of ZnO, though electrical and optical properties were inferior to those of ZnO:Al. Temperature-dependent Hall measurements of ZnO:Al films show evidence of a different scattering mechanism than ZnO:Mo films.